The present invention relates to an air pressure servomotor which has a reinforced shell and in which the stroke of the output rod is not shortened by deformation of the shell.
A prior art air pressure servomotor comprises a housing consisting of a front shell and rear shell, a valve disposed at the center of said housing and being movable axially of the servomotor, a diaphragm located around said valve and extending radially outwardly to the wall of the shell, and piston plate disposed adjacent to the diaphragm and mounted integrally a said valve. A spacer means is mounted on the forward wall of the front shell by a bolt and the servomotor supports a master cylinder through the spacer. The servomotor is secured to the foot board dividing a driver's compartment and the engine space of a vehicle by means of bolts mounted on the wall of the rear shell. In a servomotor mounted on the foot board as above, the force applied to the master cylinder by a driver tramping down on the brake foot pedal must be resisted by the front and rear shells which function as a rigid body or member. However, the strength of these shells of the prior art servomotor is not sufficient to resist the force applied to the master cylinder. Therefore, the prior art servomotor has the disadvantage in that the shells are deformed as the force is applied to the master cylinder, and the stroke of the servomotor is shortened.
One way to avoid the above mentioned disadvantage is to increase the strength of the front and rear shells by making these shells thicker. But, this increases the weight of the servomotor unnecessarily and uses more material for producing the servomotor than is desirable.
It is an object of the present invention to provide an air pressure servomotor which can fully resist the force applied to the master cylinder without the necessity of making the shells thicker.